Many electronic devices benefit from being able to detect an object, such as a user, in close proximity to the electronic device. For example, the state in which an electronic device operates can be based, at least in part, on user proximity. In one approach, by detecting the absence of a user, the electronic device can operate in a power down mode. This is especially useful for battery operated devices.
Wireless communications devices are one example of an electronic device that can benefit from detecting the presence or absence of a user. Wireless communications devices have proliferated due to their convenience. However, power consumption is a major issue in such devices because many wireless communications devices are battery operated.
One conventional technique for saving power in a wireless communication device 105 is illustrated in FIG. 1. This conventional technique uses an oscillator 110 coupled to an antenna 115. When the user 120 comes into close proximity with the antenna 115 coupled to the oscillator 110, the capacitance of the oscillator antenna 115 is altered, which causes the frequency of the oscillator 110 to change. The detect/control circuit 140 detects the frequency change and increases the power to the transceiver 130. Thus, the change in oscillator frequency indicates that a user 120 is in close proximity to the oscillator antenna 115. However, this conventional technique requires the oscillator antenna 115 be physically separate from the antenna 125 of the radio transceiver 130. Electronic devices, such as wireless mice, have limited space for antennas. Thus, the two separate antennas must compete for space. Having competing antennas in a limited space has the potential to degrade performance of the radio transceiver. Moreover, the oscillator, its antenna, and associated circuitry add to the complexity and expense of the electronic device.
Conventional wireless communication devices consume more power than is desirable. Devices to limit power consumption are available, but they suffer from additional problems. Conventional power management circuitry is often complex and expensive. Moreover, the circuitry of conventional power management devices sometimes interferes with the normal operation of the device in which the power management circuitry resides.